Immunocytochemistry has proved to be a valuable diagnostic adjunct to cytopathologic diagnosis. The Cytopathology Section is involved in several clinically-related research projects, many of which utilize fine needle aspiration (FNA) and immunocytochemistry to provide ancillary diagnostic information regarding expression of various tumor antigens, HLA antigens or other markers. A partial listing of such studies includes: (1) Evaluation of percent of tumor cells expressing CD22 and CD19 in FNA specimens as part of a clinical trial using monoclonal antibody therapy for refractory lymphomas; (2) Evaluation of expression of drug resistance marker P-glycoprotein prospectively by FNA in breast cancer patients treated with new combination chemotherapy; (3) Ultrasound guided FNA of parathyroid lesions; (4) Cytologic and immunocytochemical characterization of mantle cell lymphomas; (5) Cytologic diagnosis and immunophenotyping of ocular lymphomas.